1. Field of the Invention
The present invention relates to blood pressure measuring devices or sphygomanometers and, more particularly, to a valve for the controlled release of the air from the pressurized measuring cuff of a sphygomanometer during the taking of blood pressure measurements.
2. Description of the Prior Art
The taking of blood pressure measurements by the method of Riva-Rocci and Korotkoff involves the use of an inflatable measuring cuff which is wrapped around an extremity of a person and inflated to a pressure level above the anticipated systolic blood pressure reading by means of a source of air pressure. The pressure inside the measuring cuff is then reduced in a delicately adjusted and as even as possible way, so that, when the systolic blood pressure value is approached, the onset of the so-called Korotkoff noises in the blood flow can be detected acoustically and, later, at the diastolic blood pressure value, the disappearance of these blood flow noises is reliably detected. For this purpose, an air release valve is arranged in the connecting hose between the measuring cuff and the pressure source, the air release valve comprising a flow metering device for the pressurized air, as the latter exits to the atmosphere via an outlet duct.
The various known air release valves include simple valves which have a release screw with a conical extremity that serves as a valve body in cooperation with a matchingly tapered valve seat. A disadvantage of this type of air release valve is its ergonomically unfavorable adjustment movement which requires considerable finger dexterity and skill on the part of the operator. Other known air release valves have a valve body with a very slender valve cone which cooperates with a cylindrical or likewise tapered valve seat. The valve cone is moved by means of a finger, using either a sliding lever or a pivoting lever. Both versions have the shortcoming that, in the course of the opening adjustments of the valve cone, which normally involve a linear displacement, the cross-sectional area increases as a square function of the valve displacement. Accordingly, the relatively rapid increase in the cross sectional area results in the setting of air release speeds of different magnitude, caused by uneven adjustment displacements of the valve cone, as may be necessary, for instance, in the course of measuring the interior pressure or under non-uniform initial pressure levels. The sensitivty of these air release valves is therefore not uniform over their entire operational range.